An aneurysm is a localized dilation of a blood vessel wall usually caused by degeneration of the vessel wall. These weakened sections of vessel walls can burst, causing an estimated 32,000 deaths in the United States each year. Additionally, aneurysm deaths are suspected of being underreported because sudden unexplained deaths, about 450,000 in the United States alone, are often simply misdiagnosed as heart attacks or strokes while many of them may be due to aneurysms.
U.S. surgeons treat approximately 50,000 abdominal aortic aneurysms each year, typically by replacing the abnormal section of vessel with a polymer graft in an open surgical procedure. A less-invasive procedure that has more recently been used is the placement of a stent graft at the aneurysm site. Stent grafts are tubular devices that span the aneurysm site to provide support without replacing a section of the vessel. The stent graft, when placed within a vessel at an aneurysm site, acts as a barrier between blood flow and the weakened wall of a vessel, thereby decreasing pressure on the damaged portion of the vessel. Patients whose multiple medical comorbidities make them very high risk for conventional aneurysm repair can be candidates for stent grafting.
While stent grafts can represent improvements over previously-used vessel treatment options, there are still risks associated with their use. The most common of these risks is migration of the stent graft due to matrix remodeling and/or hemodynamic forces within the vessel. Stent graft migration can lead to endoleaks, i.e., the leaking of blood into the aneurysm sac between the outer surface of the graft and the inner lumen of the blood vessel, which can increase the risk of vessel rupture. Such migration of stent grafts is especially possible in curved portions of vessels where asymmetrical forces place uneven forces on the stent graft.
Based on the foregoing, one goal of treating aneurysms is to provide stent grafts that do not migrate. To achieve this goal, stent grafts with stainless steel anchoring barbs that engage the vessel wall have been developed. Additionally, endostaples that fix stent grafts more securely to the vessel wall have been developed. While these physical anchoring devices have proven to be effective in some patients, they have not sufficiently ameliorated stent graft migration associated with current treatment methods in all cases.
An additional way to reduce the risk of stent graft migration is to administer to the treatment site, either before, during or relatively soon after implantation, one or more growth factors. The administration of one or more growth factors can be beneficial because, normally, the material of the stent graft does not provide a hospitable environment for cells in the area to grow. As a result, the stent graft rests against the vessel wall and may not be incorporated into the vessel wall. If one or more growth factors are administered immediately before, during or relatively soon after stent graft deployment and implantation, the smooth muscle cells and fibroblasts will be stimulated to proliferate. As these cells proliferate they can grow around the stent graft such that the device becomes physically attached to the vessel wall rather than merely resting against it.
Co-pending U.S. patent application Ser. No. 10/977,545, to which this application claims priority and which is fully incorporated by reference herein, describes promoting cell growth with autologous platelet gel (APG). This method provides numerous benefits that reduce the overall likelihood of stent graft migration and endoleak. It has been noted, however, that in some instances, after application at an aneurysm treatment site, the APG can retract from its original deposition volume. Thus, while the risk of stent graft migration and endoleak is reduced overall, when this retraction occurs, a small potential for endoleak is re-created. Thus, there is room for further improvement in administering APG at aneurysm sites to even further reduce the risk of endoleak. Embodiments according to the present invention address this opportunity by providing methods to reduce the likelihood of APG retraction at aneurysm sites.